Phenanthrene derivatives for use in liquid-crystalline mixtures have already been disclosed in DE-A 19500768, WO 98/27043, WO 98/27035 or WO 99/24385.
However, since the development of liquid-crystal mixtures can in no way be regarded as complete, display manufacturers are interested in a wide variety of components for mixtures.
In particular, liquid-crystal mixtures are required which have a very broad operating temperature range, but also a very low threshold voltage, for example for use in automobiles, in which a temperature range from xe2x88x9240 to 100xc2x0 C. can easily occur, but also for portable devices such as mobile telephones and notebook PCs.
There is thus a continuing demand for novel, suitable liquid-crystal mixtures and mixture components.
The present invention thus provides novel components for use in nematic or cholesteric liquid-crystal mixtures which have positive dielectric anisotropy values combined with a favorable viscosity/clearing point ratio. Moreover, the compounds should have a high light and UV stability and thermal stability. They should furthermore be suitable for realizing high voltage holding ratios (VHR). They should also be readily obtainable synthetically and thus potentially inexpensive.
It has now been found that these requirements are satisfied by hydrogenated phenanthrenes of the formula (I) 
in which:
R1 is H, an alkyl radical having 1 to 12 carbon atoms or an alkenyl radical having 2 to 8 carbon atoms, where, in each case, one (nonterminal) xe2x80x94CH2xe2x80x94 group may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94C(=O)Oxe2x80x94 or xe2x80x94OC(=O) and/or one or more H may be replaced by F,
R2 is H, F, an alkyl or alkoxy radical having 1 to 12 carbon atoms or an alkenyl or alkenyloxy radical having 2 to 8 carbon atoms, where, in each case, one (nonterminal) xe2x80x94CH2xe2x80x94 group may be replaced by xe2x80x940xe2x80x94 or xe2x80x94C(xe2x95x90O)Oxe2x80x94 and/or one or more H may be replaced by F,
M1 is xe2x80x94C(xe2x95x90O)Oxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CH2CH2 or a single bond,
m, n are each, independently of one another, zero or 1; m+n being 0 or 1,
p, q are each, independently of one another, zero or 1; p+q being 1 or 2,
Preference is given to the compounds of the formulae (Ia) to (Im): 
When designating the compounds, the letters j and l were omitted since they might be confused with i and I.
Very particular preference is given to those compounds of the formulae (Ia), (Ib), (Ie), (Ig), (Ih), (Ii) and (Ik) in which R2 is:
a) F,
b) an alkyl or alkyloxy radical having 1 to 2 carbon atoms in which one or more H are replaced by F, or
c) an alkenyl or alkenyloxy radical having 2 carbon atoms in which one or more H are replaced by F.
Special preference is given to the compounds of the formulae (Ii1), (Ig1), (Ib1) and (Ie1) 
The compounds of the formula (I) are used in liquid-crystal mixtures, preferably in nematic or cholesteric liquid-crystal mixtures. The liquid-crystal mixtures of the invention comprise at least one compound of the formula (I), preferably in an amount of 1 to 40% by weight, based on the liquid-crystal mixture. They preferably comprise at least 3 further components. The invention also provides a liquid-crystal display containing these liquid-crystal mixtures.
Typical liquid crystal mixtures are disclosed in, e.g., U.S. Pat. No. 5,378,395. Typical displays, in which these mixtures are used are AMD displays, e.g., TN-TFT displays, IPS-TFT displays and VAN-TFT displays, among various others.
The compounds of the invention can be prepared as follows: 
The synthesis according to Scheme 1 as illustrated for a specific compound can be applied broadly to the synthesis of the compounds according to the invention by varying the fluoro compound (II) or the alkyl chains of the cyclohexylamino compounds (III) or by replacing the alkyl substituent in (III) by a 4-alkylcyclohexyl radical.
For example, replacement of 2-(2,3,4-trifluoro-phenyl)ethyl bromide (prepared similarly to the method of R. P. Houghton, M. Voyle, R. Price, J. Chem. Soc. Perkin Trans 1 (1984), 92 5) by 2-(2,3-difluoro-phenyl)ethyl bromide [126163-29-9] may lead to compounds of the formula (Id) or (Ih) in which R2 is F; likewise, compounds of the formula (Id) or (Ih) in which R2 =H can be obtained by using 2-(2-fluoro-phenyl)ethyl bromide [91319-54-9] as (II). The subsequent ortho metalation reactions described below can be applied to the compounds obtained.
Process variations for the synthesis of intermediate (X) are described in T. Cuvigny, H. Normant, Organometallics Chem. Synth., 1 (1971) 237, and T. Takeda, H. Taguchi, T. Fujiwara, Tetrahedron Lett. 41 (2000) 65.
Another possible synthesis route, likewise illustrated for a specific compound, is shown in Scheme 2. However, those skilled in the art will recognize that replacement of the fluorinated tetralone (IV) [1101931-79-8] by 7-fluoro-1-tetralone [2840-44-0] will lead to compounds of the formula (Ik) or (Im), while compounds of the formula (Ih) or (If) can be obtained by using 5-fluoro-1-tetralone [93742-85-9]. It is also known that the substituent R1 of the compounds according to the invention can be varied by varying the alkyl halide in reaction step d).
Starting from (V), those skilled in the art can introduce the substituent R2 in the form of an alkyl group in accordance with standard ortho metalation methods, e.g. using xe2x80x9cSchlosser basexe2x80x9d; alternatively, the lithium compound which is initially formed can be converted into the corresponding boronic acid by means of boric esters, and this boronic acid can in turn be oxidized to give the corresponding 2-hydroxyphenanthrene derivative. The latter can be transformed by Williamson ether synthesis into compounds of the formula (Ii) [or, similarly, (Ig)] in which R2 is an alkyloxy group; compounds of the formula (I) in which M1 is xe2x80x94OC(xe2x95x90O)xe2x80x94 can be obtained by esterification. 
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.
The entire disclosure of all applications, patents and publications, cited above or below, and of corresponding German application No. 100 28 451.5, filed Jun. 8, 2000, is hereby incorporated by reference.
All temperature differences are difference degrees Celsius. All physical properties are given for 20xc2x0 C., the refractive indices are given for a wavelength of 589 nm, and the dielectric anisotropies are given for a frequency of 1 kHz.